Silicones, alginates and hydrocolloids are used in the production of working models in dental engineering and also in the production of precise impressions and temporary dental prostheses in dentistry. For example, U.S. Pat. No. 4,778,832 describes silicone compositions, which contain hydrophilic silicone oils or non-ionic surfactants to make the compositions hydrophilic. As non-ionic surfactants, inter alia, polyethers and partial esters of polyalcohols and fatty acids come into consideration.
For particularly precise work, polyether impression materials are used. Such impression materials generally consist of polyalkylene oxides, in which the end groups are derivatized with polymerizable compounds. For example, the U.S. Pat. Nos. 3,453,242 and 4,093,555, DE-PS-1 544 837 and DE-OS 32 46 654, describe aziridine-containing polyalkylene oxides for this use. The aziridine containing compounds are generally used in conjunction with fillers, colorants and other auxiliary agents, such as, for example, plasticizers.
For the initiation of the polymerization reaction, e.g., from U.S. Pat. No. 4,167,618, sulphonium salts are known, which contain an electron-attracting group in the beta-position to the central sulfur atom and a non-nucleophilic anion.
So-called plasticizers and solubilizers are usually added to the aziridine-containing compounds and the component which contains the catalyst to regulate the processing properties and the plastic/elastic behavior. Hydroxy-functional poly-alkylene oxides, such as the copolymers of ethylene oxide and propylene oxide, phthalates, such as, e.g., dioctyl phthalate, citrates, such as e.g., acetyl trialkyl citrate, and toluene and dibenzyl toluene have, for example, been described for this use.
The use of such compounds is also known from other fields. For example, British Patent reference GB-PS 621 104 describes the use of polyalkylene oxides and polyalkylene oxide glycols as surfactants in dye dispersions and the like. German Patent reference DE-OS 37 12 646 explains the use of alkyl-polyalkylene carboxyl compounds as essential constituents in skin-care preparations and German Patent reference DE-OS 37 02 178 refers to the use of polyglycerine ethers as skin-compatible additives in cosmetic and pharmaceutical preparations.
The polyether impression materials are usually stored in the form of two spatially separate components until they are actually used. The reactive impression material is then formed by intensive mixing and hardens in a few minutes. Here one component contains the polyether, e.g., the aziridine-containing compound, and the other component the catalyst, e.g, the sulphonium salts. Since relatively high-molecular-weight compounds are used in the first component and relatively low-molecular-weight compounds are used in the second, the mixture ratio usually differs clearly from a mixture ratio of 1:1, even when fillers and plasticizers and also solubilizers are added.
To mix the components, in addition to mixing with a spatula on a block, the dentist has mechanical mixing aids available to him. Centrifuge mixers are known for this purpose on the one hand and on the other, it is known for the components to be homogeneously mixed with each other by static mixing. In this case, the two components are stored in double-chamber cartridges and shortly before use, are pressed through a mixing nozzle in which a static mixing element is housed. The components are mixed with each other due to the special form of the mixing spirals. In this system, the flow properties of the two components must be as similar as possible, and in addition, their chemical behavior should be so similar that immediate mixing takes place with short contact times.
To adjust a mixture ratio in polyether impression materials as would be suitable to be mixed with static mixers, it was often necessary to introduce relatively large amounts of fillers and plasticizers and/or solubilizers into the component containing the catalyst. However, with the known plasticizers and/or solubilizers, this was only partly possible because problems of storage instability occurred, particularly dissociation of the mixture, or the rheological behavior of the two components differed notably, or the two components differed chemically to such an extend that they could not be homogeneously mixed in a static mixer.